1917] MACCAUGHEY—HAWAIIAN FLORA 409 
absence of actual observations in the higher levels, a temperature 
decrease of 1° F. is assumed in each 320 ft. of ascent.” The 
annual mean summit temperature of Kea is given as below 30°. 
It should be emphasized that very much lower temperatures than 
these prevail during a considerable portion of the year, especially 
at night, and are accentuated by the high winds. During the 
brilliant cloudless day the black lava sheets absorb great quantities 
of heat, and the aerial temperatures near the ground become very 
high. At nightfall, however, a very rapid chilling of the air 
ensues, and the thermometer drops in a few hours to the neigh- 
borhood of freezing point. This sudden drop is familiar to all who 
have ascended the high peaks. This wide diurnal range of aerial 
summit temperatures is in striking contrast to the equable and 
monotonously invariable temperatures of the littoral regions. 
TEMPERATURES OF LAVA AND CINDER FIELDS.—Reference has 
already been made to the low temperatures which prevail at the 
summit regions. Another phase of this extremely interesting 
ecological factor remains to be considered, namely, the compara- 
tively high temperatures which characterize the lava and cinder 
fields themselves during the daytime. All of these volcanic deposits 
are black or very dark in color. They absorb vast quantities of 
heat during the uninterrupted diurnal period of insolation. Those 
who have traveled across the lava waste lands well know that by 
the middle of the afternoon the surface of the rock is distressingly 
hot. The surface, the rock layer immediately below it, and the 
aerial layer immediately above it have temperatures much higher 
than the prevailing aerial temperatures. This condition is similar 
to that reported by investigators of other desert regions. Mac- 
Dovucat™ notes that ‘the sandy soil around the roots of small 
herbaceous plants in the Grand Canyon, Arizona, . . . . exhibited 
temperatures as high as 148° F.” It is to be further noted, as 
MacDoveat states (loc. cit., p. 77), that ‘‘these extreme tempera- 
tures are met only by the roots of species spreading in the surface 
layers of the soil.” Deep-rooted species are not so likely to be 
affected. 
% U.S. Weather Bureau, Hawaii Station, Ann. Rept. 1915 (p- 2). 
 MacDoveat, D. T., Botanical features of American deserts, p. 82. 
